The bottom pivot broke

Looking at your photos, I believe the 79-127 could be the part you need. Take a look to see what you think. Also take note that removing that bottom threshold pivot will be a job. Use plenty of a spray lubricant like a WD-40 and be prepared to drill out the screws in the threshold. You could also try to get a "flat bar" and try to lift up the threshold where the screws are if you can't remove them with an electric screw gun.